The present invention relates to a type of pressure vessel and more particularly, to a pressure vessel having a non-circular axial cross-section to be used either as an aircraft engine duct or as an aircraft fuel tank. The use of pressure vessels is particularly important with respect to aircraft engine ducts and fuel tanks since an engine duct or fuel tank having an elliptical-shaped axial cross-section is aerodynamically less protrusive than an equivalent circular cross-sectional vessel. Certain problems, however, result from the vessel's non-circular axial cross-sectional configuration. Where the internal pressure forces in a circular pressure vessel create simple "hoop" tension forces in the walls of a "circular" pressure vessel, the walls of a "non-circular" pressure vessel become subject to varying bending moments around the periphery. The bending moments result from the non-circular section tending to become round under the internal pressure, with the bending moments being maximum at the nose and tending to "open up" the nose curvature, reducing to zero, then reversing the bending direction at the top and bottom centerlines.
In the conventional approach to dealing with these bending loads, internal or external frames have been added to the non-circular pressure vessel. These frames are generally added around the entire surface periphery of the pressure vessel, and are closely-spaced along the entire length, thereby greatly increasing the weight and cost of the pressure vessel. An additional disadvantage of using these frames is the deflection of the shell's skin between each of the frame members in the presence of pressure This skin deflection increases aerodynamic drag, and thereby reduces propulsion efficiency, thus again necessitating close spacing of the frames leading to increased weight and cost.
An object of the present invention is to provide a non-circular pressure vessel that avoids the use of support frames and their corresponding disadvantages. An additional objective of the present invention is to provide a non-circular pressure vessel with essentially constant compression and tension loads around the periphery despite the varying bending moments created by the non-circular cross-sectional axial configuration. A further objective is to provide a non-circular pressure vessel that is able to carry fuselage axial compression and bending loads resulting from its attachment to the fuselage. A further objective of the present invention is to provide a non-circular pressure vessel that has minimal weight and maximum aerodynamic smoothness, and which may be constructed with minimal cost and with improved reliability.